The present application relates to an optical sensor device that can detect directional and non-directional light, for example ultra-violet light.
Light reaching an optical sensor can be either direct, which means it comes directly from the light source and is not scattered, or it can be non-directional or ambient, which means that it is scattered. For the present application the light source can be, for example, the sun. Therefore, on a clear day with no clouds, nearly all of the light coming from the sun to the sensor is direct and not scattered. However, on a cloudy day most of the light reaching the sensor is scattered and comes from different directions. In order to measure the intensity of, for example, ultra-violet light, for different surrounding light conditions or different weather conditions it is necessary to detect light that comes from different directions.
A known solution for detecting ultra-violet light is employing an interference filter on top of an optical sensor. The interference filter requires the incident light to be perpendicular towards the light-sensitive surface or nearly perpendicular to this surface. In order to limit the range of incidence angles of the light a diffuser with an air gap is employed. With the diffuser only light with an incidence angle close to 90° towards the light-sensitive surface is passed to the sensor.
However, this arrangement with the diffuser and the air gap requires a certain package height of the sensor structure. Furthermore, in this arrangement the signal that should be detected is attenuated by the diffuser. This means that the optical sensor has to be very sensitive to also detect the attenuated signal.